User blog comment:CelestialCheese/Celestial's Egg and Pokemon Mart/@comment-31308142-20170221210234/@comment-26120508-20170224215117

It depends on the item

Mega Stones = Eevee, Bagon, another egg of your choice

Rare Bone, Heart Scale = Eevee and Bagon

Evolutionary Stones, Plates, Star Piece, Leftovers, Sawsbuck Coffee, Metronome = Bagon